lsp-mcp

An MCP server that exposes a single Language Server Protocol server to agents as a headless editor.

lsp-mcp starts the language server you provide, keeps its document state in sync with the workspace, and exposes the language server's capabilities through MCP tools and resources. It is written in TypeScript and Effect, and runs directly on Node.js without a build step.

Features

stdio and Streamable HTTP MCP transports
Diagnostics exposed both as a tool and subscribable MCP resources
Preview-by-default edits for rename and formatting, with explicit disk application
Language-server crash supervision, restart backoff, and document reopening
Initialization options, workspace settings, language-id mappings, and open-document capacity configuration

Underlying techniques:

On-demand document opening, disk change detection, and an LRU cache of open documents
1-based line and column positions designed for agent-facing use
Capability-aware tool registration: unsupported LSP features are not advertised

Requirements

Node.js 26+
pnpm 12.4.2+
An installed language server executable

Installation

pnpm install

The repository runs TypeScript directly. From a checkout, invoke the server with node src/main.ts.

Usage

The general form is:

node src/main.ts [lsp-mcp options] -- <language-server> [language-server args...]

The -- separates lsp-mcp options from the executable and arguments passed to the language server.

stdio

stdio is the default transport and is suitable for MCP clients that launch a local server process:

node src/main.ts --root /path/to/project -- typescript-language-server --stdio

For example, an MCP client configuration can point at the checkout like this:

{
  "mcpServers": {
    "typescript": {
      "command": "node",
      "args": [
        "/path/to/lsp-mcp/src/main.ts",
        "--root",
        "/path/to/project",
        "--",
        "typescript-language-server",
        "--stdio"
      ]
    }
  }
}

Streamable HTTP

Run the MCP endpoint on a local port with --http:

node src/main.ts --http 9010 --root ./crate -- rust-analyzer

The endpoint is available at:

http://localhost:9010/mcp

Configuration examples

# Pass JSON initialization options to the language server.
node src/main.ts \
  --init-options '{"typescript":{"useInferredProjectPerProjectRoot":true}}' \
  -- typescript-language-server --stdio

# Serve workspace/configuration and didChangeConfiguration with JSON settings.
node src/main.ts \
  --settings '{"gopls":{"staticcheck":true}}' \
  -- gopls

# Add a file-extension to language-id mapping.
node src/main.ts --language vue=vue --root ./web -- vue-language-server --stdio

# Keep more documents open, and always restart a crashed language server.
node src/main.ts --open-documents 64 --restart always -- clangd

Development

pnpm test   # Run the Vitest suite, including the fixture LSP integration tests
pnpm check  # Type-check without emitting JavaScript
pnpm lint   # Format and lint with Biome

The main source layout is:

src/Model.ts      Agent-facing schemas and 1-based positions
src/Tools.ts      MCP tool definitions and capability gating
src/Resources.ts  MCP resources and notifications
src/Server.ts     Effect layer composition and transports
src/main.ts       CLI entry point
src/lsp/          LSP process, document, diagnostic, and editor bridge
test/             Unit and integration tests with a fixture language server

The vscode-* packages are intentionally confined to src/lsp/; the rest of the application uses the agent-facing schemas and Effect services.

License

MIT

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